An oil shale refers to a fine-grained sedimentary rock with high kerogen content and can be fractionated into a considerable amount of oils, and also refers to a solid combustible organic with more than 40% of ashes in percentage by weight and oil content ranging from 3.5% to 30%. The oil shale has more than 40% of ashes in percentage by weight compared to coals.
The oil shale must be heated to discharge hydrocarbon gases and fluids. For over 100 years, the oil shale is exploited by several ways worldwide, including on-ground processing, underground processing and combined processing. The on-ground processing includes mainly three steps such as oil shale exploitation and ore preparation, kerogen produced by thermal decomposition, and refined raw materials and usable chemicals produced by processing the kerogen, wherein it is known to commonly use a “underground exploitation and on-ground retorting” technique and a “on-ground exploitation and on-ground retorting” technique. With regard to the former, oil shale ores are exploited, conveyed to the ground surface and crushed, and then heated the processed ores in a container on the ground surface to produce fuel liquids and gases; and with regard to the latter, the oil shale ores are opencast, and then are subjected to crushing and retorting. The processed slag is accumulated in a mine field or other locations. As for the underground processing, oil shale resources are heated in a natural deposition environment of the oil shale to produce kerogen, thereby minimizing or eliminating exploitation procedures and thermal decomposition on the ground surface. Heats for previously achieving an underground temperature for thermal decomposition come from combustion at one end of oil shale accumulation while today, for example, it is attempted to accelerate heat transfer and fluid flow in the oil shale by fracturing a shale bed, thereby improving thermal decomposition efficiency and oil recovery in underground combustion. As for combined processing, near-surface oil shale resources are processed on the ground surface and then slow heating is performed in pits formed by excavating rocks for underground exploitation.
Although the exploitation, processing, utilization and the like of the oil shale has been advanced worldwide, many problems including improvement of energy efficiency and reduction of energy demands, minimization of water consumption and protection of surface water and underground water due to the on-ground processing and the underground processing, decrement, utilization and disposal of discarded slag, development of infrastructures to meet various demands to energy and mineral resources, and reduction of risks, mitigation and settlement of potential social economic factor, etc. still exist. The exploitation of the oil shale must be enforced due to global energy shortages.
The conventional oil shale exploitation method has the disadvantages of high technical energy consumption, low economic efficiency, serious pollution to underground water, and complicated processes.